Important cave notions

The Cave represents the dream descent into the unconscious, where that which is repressed and ignored will come to be seen in full light.
The price of admission is a reversal of normal conduct and ideas associated with waking life.
The cave often contains the dead and sometimes spirit animals. The animals give strength and the dead often mock the heroes who have become 'as weak as they.'
The cave is ubiquitous in popular literature and cinema, but exists in the bible generally as temporary blindness and a few times as a pit that leads to hell.
What is in the cave is not just darkness, however, there is also a treasure, a golden light that symbolizes the effulgence of a forgotten sun. Sometimes it is in the form of knowledge of the future, sometimes it is the ability to shut up this underworld as with Jesus' keys and Luke's repression of his own dark side. If these hordes of the subconscious can be mastered, stolen or understood (if the horde is intellectual knowledge), then the hero can ascend back to the surface, or emerge from the bottom of the cave (as it is with Dante, being shit out by the devil) and use this hidden treasure of the deep to redefine and reestablish life on the surface, or waking life.
For more information, please look at my blog on Etruscan divination, where I have explored some of these notions of Frye's in more detail, within the context of how the Etruscans saw the future.